Portuguese Interior Minister Eduardo Cabrita on Friday announced his resignation after his work vehicle was involved in a fatal crash.
Cabrita said he would not allow the "absolutely unacceptable political exploitation" of the accident to damage Prime Minister Antonio Costa or his Socialist Party (PS) ahead of the parliamentary election on January 30.
A few hours earlier, it had emerged that the public prosecutor's office would file charges of negligent homicide against his driver.
Cabrita was sitting in the car when the vehicle hit and killed a motorway worker on June 18.
The car was travelling at 166 kilometres per hour, media reported citing judicial sources. Portugal's motorways have a speed limit of 120 kilometres per hour.
The accident occurred at a signposted construction site.
The 60-year-old minister initially tried to absolve himself of any responsibility on Friday. "I was only a passenger," he said.
However, this triggered a wave of indignation.
Announcing his resignation in the evening, he stressed that he regretted the tragedy and expressed his condolences to the victim's relatives and friends.